Virtual point in time access between snapshots

ABSTRACT

A System, Computer program product, and computer-executable method for providing a user access to an image of data storage, wherein the data storage is managed by a data protection appliance (DPA), the System, Computer program product, and computer-executable including receiving a request for the image of data storage, wherein the image requested is the data storage at a Point in Time (PiT), creating a virtual image of data storage using a difference journal, wherein the virtual image provides the user with access to data within the requested image at the PiT, and providing access to the virtual image.

A portion of the disclosure of this patent document may contain commandformats and other computer language listings, all of which are subjectto copyright protection. The copyright owner has no objection to thefacsimile reproduction by anyone of the patent document or the patentdisclosure, as it appears in the Patent and Trademark Office patent fileor records, but otherwise reserves all copyright rights whatsoever.

TECHNICAL FIELD

This invention relates generally to data backups, and more particularlyto continuous data replication on deduplicated storage.

BACKGROUND

Computer data is vital to today's organizations, and a significant partof protection against disasters is focused on data protection. Assolid-state memory has advanced to the point where cost of memory hasbecome a relatively insignificant factor, organizations can afford tooperate with systems that store and process terabytes of data.

Conventional data protection systems include backup drives for storingorganizational production site data on a periodic basis. Such systemssuffer from several drawbacks. First, they may require a system shutdownduring backup since the data being backed up cannot be used during thebackup operation. Second, they limit the points in time to which theproduction site can recover. For example, if data is backed up on adaily basis, there may be several hours of lost data in the event of adisaster. Third, the data recovery process itself may take a long time.

Another conventional data protection system uses data replication, bycreating a copy of the organization's production site data on asecondary backup storage system, and updating the backup with changes.The backup storage system may be situated in the same physical locationas the production storage system, or in a physically remote location.

SUMMARY

A System, Computer program product, and computer-executable method forproviding a user access to an image of data storage, wherein the datastorage is managed by a data protection appliance (DPA), the System,Computer program product, and computer-executable including receiving arequest for the image of data storage, wherein the image requested isthe data storage at a Point in Time (PiT), creating a virtual image ofdata storage using a difference journal, wherein the virtual imageprovides the user with access to data within the requested image at thePiT, and providing access to the virtual image.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, features, and advantages of embodiments disclosed herein may bebetter understood by referring to the following description inconjunction with the accompanying drawings. The drawings are not meantto limit the scope of the claims included herewith. For clarity, notevery element may be labeled in every figure. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingembodiments, principles, and concepts. Thus, features and advantages ofthe present disclosure will become more apparent from the followingdetailed description of exemplary embodiments thereof taken inconjunction with the accompanying drawings in which:

FIG. 1 is a simplified illustration of a data protection system, inaccordance with an embodiment of the present disclosure;

FIG. 2 is a simplified illustration of a write transaction for ajournal, in accordance with an embodiment of the present disclosure;

FIG. 3 is a system for initializing a backup snapshot, consistent withan embodiment of the present disclosure;

FIG. 4 is a system for synthesizing new backup snapshots, consistentwith an embodiment of the present disclosure;

FIG. 5 is a simplified illustration of a system, in accordance with anembodiment of the present disclosure;

FIG. 6 is a simplified illustration of the system as described in FIG. 5creating a virtual image, in accordance with an embodiment of thepresent disclosure;

FIG. 7 is an alternate simplified illustration of the system asdescribed in FIG. 5 creating a virtual image, in accordance with anembodiment of the present disclosure;

FIG. 8 is a simplified flowchart of a method of providing access to avirtual image on a system as described in FIG. 5, in accordance with anembodiment of the present disclosure;

FIG. 9 is a simplified flowchart of a method of creating a differencejournal using the system as described in FIG. 5, in accordance with anembodiment of the present disclosure;

FIG. 10 is an example of an embodiment of an apparatus that may utilizethe techniques described herein, in accordance with an embodiment of thepresent disclosure; and

FIG. 11 is an example of a method embodied on a computer readablestorage medium that may utilize the techniques described herein, inaccordance with an embodiment of the present disclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. While the invention is described inconjunction with such embodiment(s), it should be understood that theinvention is not limited to any one embodiment. On the contrary, thescope of the invention is limited only by the claims and the inventionencompasses numerous alternatives, modifications, and equivalents. Forthe purpose of example, numerous specific details are set forth in thefollowing description in order to provide a thorough understanding ofthe present invention. These details are provided for the purpose ofexample, and the present invention may be practiced according to theclaims without some or all of these specific details. For the purpose ofclarity, technical material that is known in the technical fieldsrelated to the invention has not been described in detail so that thepresent invention is not unnecessarily obscured.

It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system, adevice, a method, or a computer readable medium such as a computerreadable storage medium or a computer network wherein computer programinstructions are sent over optical or electronic communication links.Applications may take the form of software executing on a generalpurpose computer or be hardwired or hard coded in hardware. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention.

An embodiment of the invention will be described with reference to adata storage system in the form of a storage system configured to storefiles, but it should be understood that the principles of the inventionare not limited to this configuration. Rather, they are applicable toany system capable of storing and handling various types of objects, inanalog, digital, or other form. Although terms such as document, file,object, etc. may be used by way of example, the principles of theinvention are not limited to any particular form of representing andstoring data or other information; rather, they are equally applicableto any object capable of representing information.

Systems, processes, and methods are discussed herein for enablingcontinuous data backups to deduplicated storage. In some embodiments, aninitial backup snapshot of a source storage system may be created on thededuplicated storage using a data protection appliance. As changes aremade to the source storage system, the 10's may be continuouslycommunicated to the deduplicated storage for backup and protection.

In some embodiments, the deduplicated storage and/or data protectionappliance may maintain journals, including data journals and metadatajournals, for synthesizing new backup snapshots and/or recovering files.The journals may include DO and UNDO information compiled from IO'scommunicated from the data protection appliance to the deduplicatedstorage. These IO's may be applied to a backup snapshot to restore thesnapshot to a previous point-in-time, or may be used to synthesize a newsnapshot.

In an embodiment, data protection windows may be defined based on policyor user preference. The data protection windows may be used to maintainsnapshots and/or journals for designated periods of time. For example,short-term windows may maintain both snapshots and journals for anypoint-in-time recovery (assuming the point-in-time falls within theshort-term window). Mid-term windows, in contrast, may delete journalsbut maintain all the snapshots created during a period, and long-termwindows may delete all the journals and select snapshots. Definingdifferent protection windows may allow point-in-time recovery for filesaccessed recently, while also providing reduced storage consumption forlong-term backups.

The systems discussed herein may additionally allow backup snapshots tobe synthesized on deduplicated storage from IO's provided from multipledata protection appliance. For example, two data protection appliancesmay protect a single SAN. Each of those data protection agents mayreport IO's to the deduplicated storage, and a single backup snapshotmay be synthesized from the journals maintaining those IO's

The following non-limiting definitions may be helpful in understandingthe specification and claims:

BACKUP SITE—may be a facility where replicated production site data isstored; the backup site may be located in a remote site or at the samelocation as the production site; a backup site may be a virtual orphysical site.

CDP—Continuous Data Protection, may refer to a full replica of a volumeor a set of volumes along with a journal which allows any point in timeaccess, the CDP copy is at the same site, and maybe the same storagearray of the production site.

DATA PROTECTION APPLIANCE (“DPA”)—may be a computer or a cluster ofcomputers, or a set of processes that serve as a data protectionappliance, responsible for data protection services including inter aliadata replication of a storage system, and journaling of I/O requestsissued by a host computer to the storage system. The DPA may be aphysical device, a virtual device running, or may be a combination of avirtual and physical device.

HOST—may be at least one computer or networks of computers that runs atleast one data processing application that issues I/O requests to one ormore storage systems; a host is an initiator with a SAN; a host may be avirtual machine.

HOST DEVICE—may be an internal interface in a host to a logical storageunit.

IMAGE—may be a copy of a logical storage unit at a specificpoint-in-time.

INITIATOR—may be a node in a SAN that issues I/O requests.

JOURNAL—may be a record of write transactions issued to a storagesystem. A journal may be used to maintain a duplicate storage system,and to rollback the duplicate storage system to a previouspoint-in-time.

LOGICAL UNIT—may be a logical entity provided by a storage system foraccessing data from the storage system.

LUN—may be a logical unit number for identifying a logical unit. Mayalso refer to one or more virtual disks or virtual LUNs, which maycorrespond to one or more Virtual Machines. As used herein, LUN and LUmay be used interchangeably to refer to a LU.

PHYSICAL STORAGE UNIT—may be a physical entity, such as a disk or anarray of disks, for storing data in storage locations that can beaccessed by address.

PRODUCTION SITE—may be a facility where one or more host computers rundata processing applications that write data to a storage system andread data from the storage system; may be a virtual or physical site.

RPA—may be replication protection appliance, and is another name forDPA. An RPA may be a virtual DPA or a physical DPA.

SAN—may be a storage area network of nodes that send and receive I/O andother requests, each node in the network being an initiator or a target,or both an initiator and a target.

SOURCE SIDE—may be a transmitter of data within a data replicationworkflow. During normal operation a production site is the source side,and during data recovery a backup site is the source side. Source sidemay be a virtual or physical site.

SNAPSHOT—a snapshot may refer to an image or differentialrepresentations of an image, i.e. the snapshot may have pointers to theoriginal volume, and may point to log volumes for changed locations.Snapshots may be combined into a snapshot array, which may representdifferent images over a time period.

SPLITTER/PROTECTION AGENT—may be an agent running either on a productionhost a switch or a storage array which can intercept IO and split themto a DPA and to the storage array, fail IO redirect IO or do any othermanipulation to the IO; the splitter or protection agent may be used inboth physical and virtual systems. The splitter may be in the IO stackof a system and may be located in the hypervisor for virtual machines.May be referred to herein as an Open Replicator Splitter (ORS).

STORAGE SYSTEM—may be a SAN entity that provides multiple logical unitsfor access by multiple SAN initiators.

STREAMING—may mean transmitting data in real time, from a source to adestination, as the data is read or created.

SYNTHESIZE—may mean creating a new file using pointers from existingfiles, without actually copying the referenced data. For example, a newfile representing a volume at a points-in-time may be created usingpointers to a file representing a previous point-in-time, as wellpointers to journal representing changes to the volume

TARGET—may be a node in a SAN that replies to I/O requests.

TARGET SIDE—may be a receiver of data within a data replicationworkflow; during normal operation a back site is the target side, andduring data recovery a production site is the target side; may be avirtual or physical site.

VIRTUAL VOLUME—may be a volume which is exposed to host by avirtualization layer, the virtual volume may be spanned across more thanone site and or volumes.

VIRTUAL RPA (vRPA)/VIRTUAL DPA (vDPA)—may be a DPA running in a VM.

WAN—may be a wide area network that connects local networks and enablesthem to communicate with one another, such as the Internet.

Overview of a Backup System Using a Journaling Process

Reference is now made to FIG. 1, which is a simplified illustration of adata protection system 100, in accordance with an embodiment of thepresent invention. Shown in FIG. 1 are two sites; Site I, which is aproduction site, on the right, and Site II, which is a backup site, onthe left. Under normal operation the production site is the source sideof system 100, and the backup site is the target side of the system. Thebackup site is responsible for replicating production site data.Additionally, the backup site enables rollback of Site I data to anearlier pointing time, which may be used in the event of data corruptionof a disaster, or alternatively in order to view or to access data froman earlier point in time.

During normal operations, the direction of replicate data flow goes fromsource side to target side. It is possible, however, for a user toreverse the direction of replicate data flow, in which case Site Istarts to behave as a target backup site, and Site II starts to behaveas a source production site. Such change of replication direction isreferred to as a “failover”. A failover may be performed in the event ofa disaster at the production site, or for other reasons. In some dataarchitectures, Site I or Site II behaves as a production site for aportion of stored data, and behaves simultaneously as a backup site foranother portion of stored data. In some data architectures, a portion ofstored data is replicated to a backup site, and another portion is not.

The production site and the backup site may be remote from one another,or they may both be situated at a common site, local to one another.Local data protection has the advantage of minimizing data lag betweentarget and source, and remote data protection has the advantage is beingrobust in the event that a disaster occurs at the source side.

The source and target sides communicate via a wide area network (WAN)128, although other types of networks are also adaptable for use withthe present invention.

In accordance with an embodiment of the present invention, each side ofsystem 100 includes three major components coupled via a storage areanetwork (SAN); namely, (i) a storage system, (ii) a host computer, and(iii) a data protection appliance (DPA). Specifically with reference toFIG. 1, the source side SAN includes a source host computer 104, asource storage system 108, and a source DPA 112. Similarly, the targetside SAN includes a target host computer 116, a target storage system120, and a target DPA 124.

Generally, a SAN includes one or more devices, referred to as “nodes”. Anode in a SAN may be an “initiator” or a “target”, or both. An initiatornode is a device that is able to initiate requests to one or more otherdevices; and a target node is a device that is able to reply torequests, such as SCSI commands, sent by an initiator node. A SAN mayalso include network switches, such as fiber channel switches. Thecommunication links between each host computer and its correspondingstorage system may be any appropriate medium suitable for data transfer,such as fiber communication channel links.

In an embodiment of the present invention, the host communicates withits corresponding storage system using small computer system interface(SCSI) commands.

System 100 includes source storage system 108 and target storage system120. Each storage system includes physical storage units for storingdata, such as disks or arrays of disks. Typically, storage systems 108and 120 are target nodes. In order to enable initiators to send requeststo storage system 108, storage system 108 exposes one or more logicalunits (LU) to which commands are issued. Thus, storage systems 108 and120 are SAN entities that provide multiple logical units for access bymultiple SAN initiators.

Logical units are a logical entity provided by a storage system, foraccessing data stored in the storage system. A logical unit isidentified by a unique logical unit number (LUN). In an embodiment ofthe present invention, storage system 108 exposes a logical unit 136,designated as LU A, and storage system 120 exposes a logical unit 156,designated as LU B.

In an embodiment of the present invention, LU B is used for replicatingLU A. As such, LU B is generated as a copy of LU A. In one embodiment,LU B is configured so that its size is identical to the size of LU A.Thus for LU A, storage system 120 serves as a backup for source sidestorage system 108. Alternatively, as mentioned hereinabove, somelogical units of storage system 120 may be used to back up logical unitsof storage system 108, and other logical units of storage system 120 maybe used for other purposes. Moreover, in certain embodiments of thepresent invention, there is symmetric replication whereby some logicalunits of storage system 108 are used for replicating logical units ofstorage system 120, and other logical units of storage system 120 areused for replicating other logical units of storage system 108.

System 100 includes a source side host computer 104 and a target sidehost computer 116. A host computer may be one computer, or a pluralityof computers, or a network of distributed computers, each computer mayinclude inter alia a conventional CPU, volatile and non-volatile memory,a data bus, an I/O interface, a display interface and a networkinterface. Generally a host computer runs at least one data processingapplication, such as a database application and an e-mail server.

Generally, an operating system of a host computer creates a host devicefor each logical unit exposed by a storage system in the host computerSAN. A host device is a logical entity in a host computer, through whicha host computer may access a logical unit. In an embodiment of thepresent invention, host device 104 identifies LU A and generates acorresponding host device 140, designated as Device A, through which itcan access LU A. Similarly, host computer 116 identifies LU B andgenerates a corresponding device 160, designated as Device B.

In an embodiment of the present invention, in the course of continuousoperation, host computer 104 is a SAN initiator that issues I/O requests(write/read operations) through host device 140 to LU A using, forexample, SCSI commands. Such requests are generally transmitted to LU Awith an address that includes a specific device identifier, an offsetwithin the device, and a data size. Offsets are generally aligned to 512byte blocks. The average size of a write operation issued by hostcomputer 104 may be, for example, 10 kilobytes (KB); i.e., 20 blocks.For an I/O rate of 50 megabytes (MB) per second, this corresponds toapproximately 5,000 write transactions per second.

System 100 includes two data protection appliances, a source side DPA112 and a target side DPA 124. A DPA performs various data protectionservices, such as data replication of a storage system, and journalingof I/O requests issued by a host computer to source side storage systemdata. As explained in detail hereinbelow, when acting as a target sideDPA, a DPA may also enable rollback of data to an earlier point in time,and processing of rolled back data at the target site. Each DPA 112 and124 is a computer that includes inter alia one or more conventional CPUsand internal memory.

For additional safety precaution, each DPA is a cluster of suchcomputers. Use of a cluster ensures that if a DPA computer is down, thenthe DPA functionality switches over to another computer. The DPAcomputers within a DPA cluster communicate with one another using atleast one communication link suitable for data transfer via fiberchannel or IP based protocols, or such other transfer protocol. Onecomputer from the DPA cluster serves as the DPA leader. The DPA clusterleader coordinates between the computers in the cluster, and may alsoperform other tasks that require coordination between the computers,such as load balancing.

In the architecture illustrated in FIG. 1, DPA 112 and DPA 124 arestandalone devices integrated within a SAN. Alternatively, each of DPA112 and DPA 124 may be integrated into storage system 108 and storagesystem 120, respectively, or integrated into host computer 104 and hostcomputer 116, respectively. Both DPAs communicate with their respectivehost computers through communication lines such as fiber channels using,for example, SCSI commands.

In accordance with an embodiment of the present invention, DPAs 112 and124 are configured to act as initiators in the SAN; i.e., they can issueI/O requests using, for example, SCSI commands, to access logical unitson their respective storage systems. DPA 112 and DPA 124 are alsoconfigured with the necessary functionality to act as targets; i.e., toreply to I/O requests, such as SCSI commands, issued by other initiatorsin the SAN, including inter alia their respective host computers 104 and116. Being target nodes, DPA 112 and DPA 124 may dynamically expose orremove one or more logical units.

As described hereinabove, Site I and Site II may each behavesimultaneously as a production site and a backup site for differentlogical units. As such, DPA 112 and DPA 124 may each behave as a sourceDPA for some logical units and as a target DPA for other logical units,at the same time.

In accordance with an embodiment of the present invention, host computer104 and host computer 116 include protection agents 144 and 164,respectively. Protection agents 144 and 164 intercept SCSI commandsissued by their respective host computers, via host devices to logicalunits that are accessible to the host computers. In accordance with anembodiment of the present invention, a data protection agent may act onan intercepted SCSI commands issued to a logical unit, in one of thefollowing ways:

Send the SCSI commands to its intended logical unit.

Redirect the SCSI command to another logical unit.

Split the SCSI command by sending it first to the respective DPA. Afterthe DPA returns an acknowledgement, send the SCSI command to itsintended logical unit.

Fail a SCSI command by returning an error return code.

Delay a SCSI command by not returning an acknowledgement to therespective host computer.

A protection agent may handle different SCSI commands, differently,according to the type of the command. For example, a SCSI commandinquiring about the size of a certain logical unit may be sent directlyto that logical unit, while a SCSI write command may be split and sentfirst to a DPA associated with the agent. A protection agent may alsochange its behavior for handling SCSI commands, for example as a resultof an instruction received from the DPA.

Specifically, the behavior of a protection agent for a certain hostdevice generally corresponds to the behavior of its associated DPA withrespect to the logical unit of the host device. When a DPA behaves as asource site DPA for a certain logical unit, then during normal course ofoperation, the associated protection agent splits I/O requests issued bya host computer to the host device corresponding to that logical unit.Similarly, when a DPA behaves as a target device for a certain logicalunit, then during normal course of operation, the associated protectionagent fails I/O requests issued by host computer to the host devicecorresponding to that logical unit.

Communication between protection agents and their respective DPAs mayuse any protocol suitable for data transfer within a SAN, such as fiberchannel, or SCSI over fiber channel. The communication may be direct, orvia a logical unit exposed by the DPA. In an embodiment of the presentinvention, protection agents communicate with their respective DPAs bysending SCSI commands over fiber channel.

In an embodiment of the present invention, protection agents 144 and 164are drivers located in their respective host computers 104 and 116.Alternatively, a protection agent may also be located in a fiber channelswitch, or in any other device situated in a data path between a hostcomputer and a storage system. Additionally or alternatively, theprotection agent may be installed as part of the storage array IO stack.In some embodiments the DPA may be installed as a virtual appliance oras a set of processes inside the storage array.

What follows is a detailed description of system behavior under normalproduction mode, and under recovery mode.

In accordance with an embodiment of the present invention, in productionmode DPA 112 acts as a source site DPA for LU A. Thus, protection agent144 is configured to act as a source side protection agent; i.e., as asplitter for host device A. Specifically, protection agent 144replicates SCSI I/O requests. A replicated SCSI I/O request is sent toDPA 112. After receiving an acknowledgement from DPA 124, protectionagent 144 then sends the SCSI I/O request to LU A. Only after receivinga second acknowledgement from storage system 108 may host computer 104initiate another I/O request.

When DPA 112 receives a replicated SCSI write request from dataprotection agent 144, DPA 112 transmits certain I/O informationcharacterizing the write request, packaged as a “write transaction”,over WAN 128 to DPA 124 on the target side, for journaling and forincorporation within target storage system 120.

DPA 112 may send its write transactions to DPA 124 using a variety ofmodes of transmission, including inter alia (i) a synchronous mode, (ii)an asynchronous mode, and (iii) a snapshot mode. In synchronous mode,DPA 112 sends each write transaction to DPA 124, receives back anacknowledgement from DPA 124, and in turns sends an acknowledgement backto protection agent 144. Protection agent 144 waits until receipt ofsuch acknowledgement before sending the SCSI write request to LU A.

In asynchronous mode, DPA 112 sends an acknowledgement to protectionagent 144 upon receipt of each I/O request, before receiving anacknowledgement back from DPA 124.

In snapshot mode, DPA 112 receives several I/O requests and combinesthem into an aggregate “snapshot” of all write activity performed in themultiple I/O requests, and sends the snapshot to DPA 124, for journalingand for incorporation in target storage system 120. In snapshot mode DPA112 also sends an acknowledgement to protection agent 144 upon receiptof each I/O request, before receiving an acknowledgement back from DPA124.

For the sake of clarity, the ensuing discussion assumes that informationis transmitted at write-by-write granularity.

While in production mode, DPA 124 receives replicated data of LU A fromDPA 112, and performs journaling and writing to storage system 120. Whenapplying write operations to storage system 120, DPA 124 acts as aninitiator, and sends SCSI commands to LU B.

During a recovery mode, DPA 124 undoes the write transactions in thejournal, so as to restore storage system 120 to the state it was at, atan earlier time.

As described hereinabove, in accordance with an embodiment of thepresent invention, LU B is used as a backup of LU A. As such, duringnormal production mode, while data written to LU A by host computer 104is replicated from LU A to LU B, host computer 116 should not be sendingI/O requests to LU B. To prevent such I/O requests from being sent,protection agent 164 acts as a target site protection agent for hostDevice B and fails I/O requests sent from host computer 116 to LU Bthrough host Device B.

In accordance with an embodiment of the present invention, targetstorage system 120 exposes a logical unit 176, referred to as a “journalLU”, for maintaining a history of write transactions made to LU B,referred to as a “journal”. Alternatively, journal LU 176 may be stripedover several logical units, or may reside within all of or a portion ofanother logical unit. DPA 124 includes a journal processor 180 formanaging the journal.

Journal processor 180 functions generally to manage the journal entriesof LU B. Specifically, journal processor 180 (i) enters writetransactions received by DPA 124 from DPA 112 into the journal, bywriting them into the journal LU, (ii) applies the journal transactionsto LU B, and (iii) updates the journal entries in the journal LU withundo information and removes already-applied transactions from thejournal. As described below, with reference to FIGS. 2 and 3A-3D,journal entries include four streams, two of which are written whenwrite transaction are entered into the journal, and two of which arewritten when write transaction are applied and removed from the journal.

Reference is now made to FIG. 2, which is a simplified illustration of awrite transaction 200 for a journal, in accordance with an embodiment ofthe present invention. The journal may be used to provide an adaptor foraccess to storage 120 at the state it was in at any specified point intime. Since the journal contains the “undo” information necessary torollback storage system 120, data that was stored in specific memorylocations at the specified point in time may be obtained by undoingwrite transactions that occurred subsequent to such point in time.

Write transaction 200 generally includes the following fields:

one or more identifiers;

a time stamp, which is the date & time at which the transaction wasreceived by source side DPA 112;

a write size, which is the size of the data block;

a location in journal LU 176 where the data is entered;

a location in LU B where the data is to be written; and

the data itself.

Write transaction 200 is transmitted from source side DPA 112 to targetside DPA 124. As shown in FIG. 2, DPA 124 records the write transaction200 in four streams. A first stream, referred to as a DO stream,includes new data for writing in LU B. A second stream, referred to asan DO METADATA stream, includes metadata for the write transaction, suchas an identifier, a date & time, a write size, a beginning address in LUB for writing the new data in, and a pointer to the offset in the dostream where the corresponding data is located. Similarly, a thirdstream, referred to as an UNDO stream, includes old data that wasoverwritten in LU B; and a fourth stream, referred to as an UNDOMETADATA, include an identifier, a date & time, a write size, abeginning address in LU B where data was to be overwritten, and apointer to the offset in the undo stream where the corresponding olddata is located.

In practice each of the four streams holds a plurality of writetransaction data. As write transactions are received dynamically bytarget DPA 124, they are recorded at the end of the DO stream and theend of the DO METADATA stream, prior to committing the transaction.During transaction application, when the various write transactions areapplied to LU B, prior to writing the new DO data into addresses withinthe storage system, the older data currently located in such addressesis recorded into the UNDO stream.

By recording old data, a journal entry can be used to “undo” a writetransaction. To undo a transaction, old data is read from the UNDOstream in a reverse order, from the most recent data to the oldest data,for writing into addresses within LU B. Prior to writing the UNDO datainto these addresses, the newer data residing in such addresses isrecorded in the DO stream.

The journal LU is partitioned into segments with a pre-defined size,such as 1 MB segments, with each segment identified by a counter. Thecollection of such segments forms a segment pool for the four journalingstreams described hereinabove. Each such stream is structured as anordered list of segments, into which the stream data is written, andincludes two pointers—a beginning pointer that points to the firstsegment in the list and an end pointer that points to the last segmentin the list.

According to a write direction for each stream, write transaction datais appended to the stream either at the end, for a forward direction, orat the beginning, for a backward direction. As each write transaction isreceived by DPA 124, its size is checked to determine if it can fitwithin available segments. If not, then one or more segments are chosenfrom the segment pool and appended to the stream's ordered list ofsegments.

Thereafter the DO data is written into the DO stream, and the pointer tothe appropriate first or last segment is updated. Freeing of segments inthe ordered list is performed by simply changing the beginning or theend pointer. Freed segments are returned to the segment pool for re-use.

A journal may be made of any number of streams including less than ormore than 5 streams. Often, based on the speed of the journaling andwhether the back-up is synchronous or a synchronous a fewer or greaternumber of streams may be used.

Initializing a Backup Snapshot on Deduplicated Storage

FIG. 3 and FIG. 4 depict systems and processes for initializing a backupsnapshot on deduplicated storage consistent with an embodiment of thepresent disclosure. Before deduplicated storage can provide continuousbackup protection, it may be necessary to create an initial backupsnapshot of the source storage system. This initial backup snapshot mayrepresent the earliest point-in-time backup that may be restored. Aschanges are made to the source storage system, journal files and/or newbackups may be updated and/or synthesized to provide continuousprotection. In some embodiments, the initial backup snapshot may becreated by streaming IO's from a storage system scan to a dataprotection appliance, or by taking an initial snapshot of the storagesystem and transmitting the entire snapshot to deduplicated storage.

FIG. 3 depicts a system for creating an initial backup snapshot byscanning a source storage system and streaming IO's to the deduplicatedstorage. Data protection application 300 may comprise journal processor302, and may be in communication with deduplicated storage 304. In anembodiment, deduplicated storage 304 may be target side storage residingat a backup site. Data protection appliance 300 may be similar to dataprotection appliance 112 and/or 124, and may be responsible forstreaming IO's to deduplicated storage 304.

In an embodiment, a source storage system may be scanned and individualoffsets may be streamed to data protection appliance 300. The offsetsstreamed from the scanned system may be referred to as initializationIO's, and may be streamed sequentially to data protection appliance 300.For example, the scanned system may comprise offsets 0, 1, 2, and 3,comprising data A, B, C, and D. The initial scan may start at thebeginning of the system, and transmit offset 0, followed by offset 1, etseq.

As data protection appliance 300 receives the initialization IO's,journal processor 302 may identify the offset data and metadata, and maystream the IO's to metadata journal 306 and/or data journal 308 residingon deduplicated storage 304. Data journal 308 may comprise data storedwithin an offset, and metadata 306 may include metadata associated withthat offset. Metadata could include, for example, an offset identifier,size, write time, and device ID. These journals may then be used tosynthesize a backup snapshot on deduplicated storage 304, as discussedbelow.

In some embodiments, a scanned storage system may operate in a liveenvironment. As a result, applications may be writing to the storageconcurrently with the scan process. If an application writes to alocation that has already been streamed, the journal files andultimately the synthesized snapshot may be out of date. To address thisissue, application IO's may be streamed concurrently with theinitialization IO's if the application IO's are to an offset that hasalready been scanned. For example, consider Table 1:

Time Offset t0 t1 t2 t3 0 A A′ 1 B B′ 2 C 3 D D′

Table 1 depicts four different offsets, denoted as 0, 1, 2, and 3, andfour times, t0, t1, t2, and t3. Letters A, B, C, and D may represent thedata stored at the offsets. Time t0 may represent the offsets as theyexist when the scan begins. These offsets may be streamed to dataprotection appliance 300 sequentially from 0 to 3. At time t1, however,the data at offset 1 is modified by an application from B to B′.Similarly, at t2 the data at offset 3 changes from D to D′, and at t3the data at offset 0 changes from A to A′. If the scan transmits thedata at offset 1 before t1, B′ may be missed since the change occurredafter offset 1 was scanned and B was transmitted. Similarly, if the scanhas not reached offset 3 before t2, only D′ will be transmitted since Dno longer exists. It may therefore be beneficial to transmit applicationIO's to data protection appliance 300 if those IO's write to an offsetthat has already been scanned. If the offset has not been scanned, itmay not be necessary to transmit the application IO's because the changewill be transmitted when the scan reaches that offset.

Turning back to FIG. 3 and with continued reference to Table 1, offsetmetadata journal entries 310 and offset data journal entries 312 depictthe state of metadata journal 306 and data journal 308 after the initialscan is complete. While there are only four offsets on the scannedstorage system, there are six entries in the journal because the data inoffset 0 and 1 was modified by an application after they were scanned.They each therefore have two entries: B and B′. Segment D was modifiedafter the scan began, but before it was reached. Segment D thereforeonly has one entry: D′.

Metadata journal entries 310 and data journal entries 312 may includeall of the data necessary to synthesize a backup snapshot of the scannedstorage system. Data journal entries 312 may contain the actual datafrom the storage system: A, B, B′ C, A′ and D′. Note that data D is notin the data journal 308 since it was modified on the storage systembefore its offset was scanned and transmitted. Metadata journal entries310 may include metadata about the offsets. For example, metadatajournal entries 310 may include an offset identifier, offset length, andwrite time, and volume/device ID. In the present example, metadatajournal entries may include the entries shown in Table 2:

0. Vol A, offset = 0; size = 8 kb; time = t0 1. Vol A, offset = 8 kb;size = 8 kb; time = t0 2. Vol A, offset = 8 kb; size = 8 kb; time = t13. Vol A, offset = 16 kb; size = 8 kb; time = t0 4. Vol A, offset = 0;size = 8 kb; time = t3 5. Vol A, offset = 24 kb; size = 8 kb; time = t2

Table 2's metadata entries may correspond to the states shown inTable 1. The offset at location may be offset 0, the offset at 8 kb maybe offset 1, the offset at 16 kb may be offset 2, and the offset at 24kb may be offset 3. The subscript of each journal entries 310 alsoidentifies the offset associated with that metadata entry.

Deduplicated storage may use metadata journal 306 and data journal 308to synthesize initial backup snapshot 314. First, metadata journal 306may be queried to identify the most recent data associated with eachoffset. Next, the data may be retrieved from journal data file 308 andsynthesized into backup snapshot 314. In some embodiments, synthesizingthe backup snapshot may comprise creating and/or copying pointers ratherthan copying entire data blocks. This could be, for example, using aproduct such as EMU® DataDomain® Boost™

For example, once the initial scan is complete, data journal 308includes data A, B, B′, C, A′, and D′. A′ and B′ are the result ofapplication IO's occurring during the scan process, and thereforerepresent the present state of offsets 0 and 1. To create backupsnapshot 314, deduplicated storage may therefore retrieve A′, B′, C, andD′ from the data journal 308 and synthesize them together.

Once initial backup snapshot 314 is synthesized, journal entries 310 and312 may no longer be needed. In an embodiment, they may be removed fromdeduplicated storage 304 in order to conserve space. Alternatively, theymay remain in the journals.

The systems and processes discussed in reference to FIG. 3 enable asystem to create an initial backup snapshot. Once the initial snapshotis created, additional processes may enable continuous data protectionand point-in-time recovery. These processes will now be discussed.

Maintaining Backup Snapshots with Continuous Data Replication

With reference now to FIG. 4, a system and process for maintainingbackups using continuous data replication is discussed. As datasetsincrease in size, backing them up to remote or local backup devicesbecomes increasingly costly and complex. Additionally, traditionalbackup processes may not allow point-in-time recovery since the backupsoccur on a periodic, rather than continuous, basis. The methods andsystems discussed herein provide continuous backup protection as writesare made to a source device, thereby reducing backup cost andcomplexity, and may allowing point-in-time recovery for backed up files.

The system of FIG. 4 includes data protection appliance 400, journalprocessor 402, and deduplicated storage 404. These elements may besubstantially similar to those discussed in reference to FIG. 3.Deduplicated storage 404 may include backup snapshot 414, metadatajournal file 406, and data journal file 408. In an embodiment, backupsnapshot file 414 is synthesized in a manner substantially similar tobackup snapshot 314, and may be created using metadata journal entries410 and data journal entries 412.

As users, applications, and other processes access and use the sourcestorage system, data on that system may change and/or new data may becreated. As a result, initial backup snapshot 414 may become stale. Ifthe source storage system should fail, there is a chance that any new ormodified data may be lost. To address this concern, data protectionappliance 400 may receive and stream application IO's to deduplicatedstorage system 404 on a continuous basis, even after initial backupsnapshot 414 is synthesized. Streaming the application IO's allows thebackups on deduplicated storage 404 to remain up-to-date, withoutneeding to perform additional backups of large datasets. This may reducenetwork traffic, reduce workloads, and conserve space on deduplicatedstorage 404.

For example, new metadata entries 411 and new data journal entries 413represent IO's made after initial backup snapshot 414 was synthesized.These entries may be written to metadata journal 406 and data journal408, as shown in FIG. 4, or they may be written to separate journalfiles. In FIG. 4, data A′ and C were modified on the source storagedevice, and the journal entries therefore comprise A″ and C′.

Periodically, new backup snapshots may be synthesized from a previousbackup snapshot and new journal entries. For example, second backupsnapshot 416 may be synthesized from initial backup snapshot 414, newmetadata journal entries 411, and new data journal entries 413. Secondbackup snapshot 416 may be used to restore source storage system up tothe point-in-time the last journal entry was received. In other words,backup snapshot 416 represents a backup of the source storage system ata later timestamp than initial backup snapshot 414.

In an embodiment, synthesizing second backup journal entry 416 may besubstantially similar to synthesizing the initial backup snapshot 414.Rather than synthesizing all of the data from data journal 408, however,unchanged data may be synthesized from initial backup snapshot 414. Inan embodiment, this synthesis may comprise copying and/or creating adata pointer. For example, in FIG. 4 the solid arrows between initialbackup snapshot 414 and second backup snapshot 416 represent unchangeddata that is common between the two. In this case, only B′ and D′ remainunchanged. The dashed arrows represent new or changed data that needs tobe synthesized into second backup snapshot 416. In FIG. 4, A′ is changedto A″, C is change to C′. Synthesizing the data into second backupsnapshot 416 therefore results in A″, B′, C′, D′.

Additionally or alternatively, second backup snapshot 416 may besynthesized entirely from journal entries. Rather than synthesizingunchanged data from initial backup 414, deduplicated storage 404 mayretrieve the unchanged data from data journal entries 412. For example,B′ and D′ may be synthesized from data journal entries 412 rather thanfrom initial backup snapshot 414.

Additional backup snapshots, such as second backup snapshot 416, may becreated periodically or on demand. For example, a user policy mayspecify that new snapshots should be created every week. Additionally oralternatively, a user may be preparing to perform some risky operationson the source storage system, and may demand that a snapshot be createdin case something goes wrong. These policies may be maintained andapplied using data protection appliance 400, deduplicated storage 404,and/or an external system.

The system and processes discussed herein may enable additional backupsnapshots to be synthesized from journal entries and existing snapshots.In some embodiments, the journal entries may be application IO's whichare continuously streamed to a data protection appliance. While thesesnapshots may provide additional data protection, they may only allowdata that exists in the snapshots to be recovered. Combining snapshotsand journal files may, however, allow any point-in-time recovery.

Virtual Point in Time Access Between Snapshots

Traditionally, a replicated storage, deduplicated storage and/or dataprotection appliance provides the ability to perform recovery frompreviously stored data. Typically, a replicated storage, deduplicatedstorage and/or data protection appliance is needed when the primary datais corrupted due to an event, such as a malicious event or anon-intended event. For example, conventionally, a replicated storage,deduplication storage and/or data protection appliance can protect froman accidental deletion of a table from a database or a virus attack thatcorrupts files. Usually, a replicated storage, deduplicated storageand/or data protection appliance allows the user to choose a point intime (PiT) that is earlier than the corrupted event which is present inthe appliance's system and restore this PiT back to the primary storagerecovering the data to a non-corrupt state. Traditionally, a replicatedstorage, deduplicated storage and/or data protection appliance creates ajournal that includes all of the changes that happened throughout theuse of storage managed by the system. Typically, a replicated storage,deduplicated storage and/or data protection appliance uses a journal tocreate a virtual image to access a snapshot of a device at a specifiedtime. Traditionally, using DO and UNDO information of a journal canwaste resources than necessary during recovery operations.Conventionally, the data storage industry would benefit from being ableto efficiently access a snapshot of a device at a specified time.

In many embodiments, the current disclosure may enable a replicatedstorage, deduplicated storage and/or data protection appliance tosupport virtual image access on demand. In various embodiments, thecurrent disclosure may enable a replicated storage, deduplicated storageand/or data protection appliance to efficiently create virtual images ofa device at a point in time. In certain embodiments, the currentdisclosure may enable a replicated storage, deduplicated storage and/ordata protection appliance build a difference table which may enable thereplicated storage, deduplicated storage and/or data protectionappliance to create a virtual image of a device. In some embodiments, areplicated storage, deduplicated storage and/or data protectionappliance may be referred to as a system and/or data storage system. Invarious embodiments, other than deduplication, a replicated storagesystem may be enabled to include the functionality of a deduplicatedstorage system

In many embodiments, a system may be enabled to create a virtual imageusing two snapshots and a difference journal. In various embodiments, asystem may create snapshots on a periodic and/or non-periodic basis. Insome embodiments, periodically may include hourly, daily, monthly,and/or other intervals. In certain embodiments, a system may be enabledto create a difference journal which may be enabled to describedifferences between a first snapshot and a second snapshot.

In many embodiments, a difference journal may be more efficient than afull journal (including DO and UNDO information) as the differencejournal may not include changes that already appear in either a firstsnapshot or second snapshot as the difference journal. In variousembodiments, reducing the size of a journal required to create a virtualimage may increase the storage efficiency of the system and the speed atwhich the system may be enabled to create the virtual image. In mostembodiments, a difference journal may include metadata from the fulljournal data and may include data for locations that have been writtenbetween a first snapshot and a second snapshot. In various embodiments,a difference journal may include data from the full journal data thatmay not already been included in the first snapshot or the secondsnapshot.

In some embodiments, a system may be enabled to create a differencejournal from a full journal once two or more snapshots are created. Forexample, in an embodiment, a system may analyze DO information from afull journal between a first and second snapshot. In this embodiment,the DO information contains data changes for four offsets and looks likeTable 3 below:

Timestamp 1 2 3 4 5 Offset 2 4 4 4 2 Data E G H I F

In this embodiment, the DO information contains information regardingchanges to the first snapshot at each timestamp specified within the DOinformation. At Time=1, Offset 2 was changed to E. At Time=2, Offset 4was changed to G. At Time=3, Offset 4 was changed to H. At Time=4,Offset 4 was changed to I and at time=5, offset 2 was changed to F. Thesystem migrates changes from the DO information to the DifferenceJournal if the DO information shows more than one data change. As shownin Table 3, Offsets 2 and 4 have changed at least two times. Further,the system does not migrate the last data change for each offset in theDO information to the Difference Journal as that information iscontained with the second snapshot. The completed difference table basedon Table 3 should like table 4 below:

Timestamp 1 2 3 4 5 Offset 2 4 4 4 2 Data E G HAs shown in table 4, the difference journal does not store data for thechanges at Time=4 and Time=5 as described above.

In most embodiments, a system may be tasked with creating periodicsnapshots of storage managed by the system. In various embodiments,while a system may be managing storage, the system may continuallycreate a full journal which may include DO and UNDO information. In someembodiments, once a first snapshot and a second snapshot is created, thesystem may convert a full journal referencing data between, andincluding, the first and second snapshots into a difference journal. Incertain embodiments, once a difference journal has been created, asystem may remove the full journal associated with the differencejournal. In most embodiments, as a system continues to create snapshots,the system may convert the full journal into a difference journal fordata between, and including, the most recent snapshot and the snapshotprior to the most recent snapshot.

In various embodiments, a system may receive requests to create avirtual image at a point in time. In certain embodiments, a system maydetermine which snapshots and/or difference journals may be applicableto the request for a virtual image at a specified point in time.

For example, in an embodiment, a system receives a request to create avirtual image at a specified point in time. In this embodiment, a systemdetermines that snapshot S1, snapshot S2, and difference Journal D1 arerelevant to the request. Subsequently, the system creates a structurethat contains references to the most recent information related to datalocations that have changed between snapshot S1 and the requested pointin time. The most recent information related to data locations may belocated within the difference journal or within snapshot S2. In thisembodiment, the system is enabled to respond to the request usingsnapshot S1 and the structure. In this embodiment, a read from thecreated virtual image may be retrieved from snapshot S1, the differencejournal by using the structure, or snapshot S2 by using the structure.

Refer to the example embodiment of FIG. 5. FIG. 5 is a simplifiedillustration of a system, in accordance with an embodiment of thepresent disclosure. As shown, System 500 includes primary data storage510, deduplicated data storage 515, and Data Protection Appliances (DPA)535, 545. Host 505 uses source Protection Agent (PA) 530 to communicatewith Primary Data Storage 510 and DPA 535. Source PA 530 splits dataI/Os from Host 505 to production LU 532 and to DPA 535. DPA 535 forwardsthe received data I/O to DPA 545 using WAN 525. DPA 545 is enabled touse journal processor 550 to create and/or update LU File 555 andJournal LU 560 residing on deduplicated data storage 515. Journal LU 560includes Journal Data 565 and Difference Journal 570. In thisembodiment, Journal Processor 550 is enabled to create snapshots of LUFile 555. Snapshot 575 is a snapshot of LU File 555 at time t₀. Snapshot580 is a snapshot of LU File 555 at time t₁. Snapshot 585 is enabled tobe the next snapshot taken of LU File 555 at time t₃. In thisembodiment, once snapshot 585 is completed, Journal Processor 550 isenabled to convert portions of Full Journal 565 relating to databetween, and including, snapshot 580 and snapshot 585, to part ofdifference journal 570.

Refer to the example embodiments of FIGS. 5 and 6. FIG. 6 is asimplified illustration of the system as described in FIG. 5 creating avirtual image, in accordance with an embodiment of the presentdisclosure. In this embodiment, Host 505 requests that system 500 createan image of Production LU 532 at Time T=4. Journal Processor 550determines that Time T=4 occurs during the elapsed time between Snapshot575 and Snapshot 580. Journal Processor 550 creates virtual image datastructure 610 and populates virtual image data structure 610 withreferences to data changed since Snapshot 575. In this embodiment,virtual image data structure 610 includes references to offset 2 inDifference Journal 570 and offset 4 in Snapshot 580 which enables system500 to create image 615.

Refer to the example embodiments of FIGS. 5 and 7. FIG. 7 is analternate simplified illustration of the system as described in FIG. 5creating a virtual image, in accordance with an embodiment of thepresent disclosure. In this embodiment, Host 505 requests that system500 create an image of Production LU 532 at Time T=1. Journal Processor550 determines that Time T=1 occurs during the elapsed time betweenSnapshot 575 and Snapshot 580. Journal Processor 550 creates virtualimage data structure 610 and populates virtual image data structure 610with references to data changed since Snapshot 575. In this embodiment,virtual image data structure 705 includes references to offset 2 inDifference Journal 570 enables system 500 to create image 710.

Refer to the example embodiment of FIGS. 5 and 8. FIG. 8 is a simplifiedflowchart of a method of providing access to a virtual image on a systemas described in FIG. 5, in accordance with an embodiment of the presentdisclosure. As shown, System 500 includes primary data storage 510,deduplicated data storage 515, and Data Protection Appliances (DPA) 535,545. Host 505 uses source Protection Agent (PA) 530 to communicate withPrimary Data Storage 510 and DPA 535. System 500 receives a request atDPA 535 to create an image at a point in time (Step 800). DPA 535forwards the request to DPA 545 through WAN 525. Journal 550 creates avirtual image structure based for the requested point in time based offdifference journal 570 (Step 810). Journal Processor 550 synthesize therequested virtual image using snapshot 575 and the virtual imagestructure (Step 820), which contains references to data changed sincesnapshot 575. System 500 provides access to the virtual image throughprimary data storage 510 or deduplicated data storage 515 (Step 830).

Refer to the example embodiments of FIGS. 5 and 9. FIG. 9 is asimplified flowchart of a method of creating a difference journal usingthe system as described in FIG. 5, in accordance with an embodiment ofthe present disclosure. As shown, System 500 includes primary datastorage 510, deduplicated data storage 515, and Data ProtectionAppliances (DPA) 535, 545. DPA 545 uses Journal processor 550 is enabledto periodically create snapshots. In this embodiment, Journal processor550 has created snapshot 575 and snapshot 580. Journal Processor 550creates snapshot 585 (Step 900) and analyzes Journal LU 560 to determinewhether a difference journal should be created (Step 910). JournalProcessor 550 determines that a difference journal should be created andcreates difference journal 570 based on DO information in Full Journal565 (Step 920). Upon completion of difference Journal 570, journalprocessor 550 removes portions of full journal 565 pertaining to datachanges between snapshot 585 and snapshot 580 (Step 930). At this point,System 500 is enabled to process virtual image requests for imagesbetween snapshot 580 and snapshot 585.

General

The methods and apparatus of this invention may take the form, at leastpartially, of program code (i.e., instructions) embodied in tangiblenon-transitory media, such as floppy diskettes, CD-ROMs, hard drives,random access or read only-memory, or any other machine-readable storagemedium.

FIG. 10 is a block diagram illustrating an apparatus, such as a computer1010 in a network 1000, which may utilize the techniques describedherein according to an example embodiment of the present invention. Thecomputer 1010 may include one or more I/O ports 1002, a processor 1003,and memory 1004, all of which may be connected by an interconnect 1025,such as a bus. Processor 1003 may include program logic 1005. The I/Oport 1002 may provide connectivity to memory media 1083, I/O devices1085, and drives 1087, such as magnetic or optical drives. When theprogram code is loaded into memory 1004 and executed by the computer1010, the machine becomes an apparatus for practicing the invention.When implemented on one or more general-purpose processors 1003, theprogram code combines with such a processor to provide a uniqueapparatus that operates analogously to specific logic circuits. As such,a general purpose digital machine can be transformed into a specialpurpose digital machine.

FIG. 11 is a block diagram illustrating a method embodied on a computerreadable storage medium 1160 that may utilize the techniques describedherein according to an example embodiment of the present invention. FIG.11 shows Program Logic 1155 embodied on a computer-readable medium 1160as shown, and wherein the Logic is encoded in computer-executable codeconfigured for carrying out the methods of this invention and therebyforming a Computer Program Product 1100. Program Logic 1155 may be thesame logic 1005 on memory 1004 loaded on processor 1003 in FIG. 10. Theprogram logic may be embodied in software modules, as modules, ashardware modules, or on virtual machines.

The logic for carrying out the method may be embodied as part of theaforementioned system, which is useful for carrying out a methoddescribed with reference to embodiments shown in, for example, FIGS.1-11. For purposes of illustrating the present invention, the inventionis described as embodied in a specific configuration and using speciallogical arrangements, but one skilled in the art will appreciate thatthe device is not limited to the specific configuration but rather onlyby the claims included with this specification.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present implementations are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A computer-executable method for providing a useraccess to an image of data storage, wherein the data storage is managedby a data protection appliance (DPA), the computer-executable methodcomprising: receiving a request for the image of data storage, whereinthe image requested is the data storage at a Point in Time (PiT);creating a virtual image of data storage using a difference journal,wherein the virtual image provides the user with access to data withinthe requested image at the PiT; and providing access to the virtualimage.
 2. The computer-executable method of claim 1, further comprising:creating a difference journal from information created by the DPA,wherein the information relates to changes between a first snapshot anda second snapshot.
 3. The computer-executable method of claim 1, furthercomprising: creating a snapshot of the data storage by the DPA;determining whether the DPA manages a second snapshot of the datastorage from a PiT previous to the snapshot; and upon a positivedetermination, creating a difference journal for information between thesecond snapshot and the snapshot.
 4. The computer-executable method ofclaim 1, wherein creating comprises: creating a virtual image structurereferencing the difference journal; and synthesizing the virtual imageof the data storage at the PiT using a first snapshot as a baseline. 5.The computer-executable method of claim 1, wherein the differencejournal stores data differences between a first snapshot and a secondsnapshot, wherein if data changed a single time between the firstsnapshot and the second snapshot, the difference journal does not storethe data changed.
 6. A system, comprising: data storage in communicationwith a Data Protection Appliance (DPA); computer-executable programlogic encoded in memory of one or more computers enabled to provide auser access to an image of the data storage, wherein the data storage ismanaged by the DPA, wherein the computer-executable program logic isconfigured to for the execution of: receiving a request for the image ofdata storage, wherein the image requested is the data storage at a Pointin Time (PiT); creating a virtual image of data storage using adifference journal, wherein the virtual image provides the user withaccess to data within the requested image at the PiT; and providingaccess to the virtual image.
 7. The system of claim 6, wherein thecomputer-executable program logic is further configured to for theexecution of: creating a difference journal from information created bythe DPA, wherein the information relates to changes between a firstsnapshot and a second snapshot.
 8. The system of claim 6, wherein thecomputer-executable program logic is further configured to for theexecution of: creating a snapshot of the data storage by the DPA;determining whether the DPA manages a second snapshot of the datastorage from a PiT previous to the snapshot; and upon a positivedetermination, creating a difference journal for information between thesecond snapshot and the snapshot.
 9. The system of claim 6, whereincreating comprises: creating a virtual image structure referencing thedifference journal; and synthesizing the virtual image of the datastorage at the PiT using a first snapshot as a baseline.
 10. The systemof claim 1, wherein the difference journal stores data differencesbetween a first snapshot and a second snapshot, wherein if data changeda single time between the first snapshot and the second snapshot, thedifference journal does not store the data changed.
 11. A computerprogram product for providing a user access to an image of data storage,wherein the data storage is managed by a data protection appliance(DPA), the computer program product comprising: a non-transitorycomputer readable medium encoded with computer-executable code, the codeconfigured to enable the execution of: receiving a request for the imageof data storage, wherein the image requested is the data storage at aPoint in Time (PiT); creating a virtual image of data storage using adifference journal, wherein the virtual image provides the user withaccess to data within the requested image at the PiT; and providingaccess to the virtual image.
 12. The Computer program product of claim11, wherein the code is further configured to enable the execution of:creating a difference journal from information created by the DPA,wherein the information relates to changes between a first snapshot anda second snapshot.
 13. The Computer program product of claim 11, whereinthe code is further configured to enable the execution of: creating asnapshot of the data storage by the DPA; determining whether the DPAmanages a second snapshot of the data storage from a PiT previous to thesnapshot; and upon a positive determination, creating a differencejournal for information between the second snapshot and the snapshot.14. The Computer program product of claim 11, wherein creatingcomprises: creating a virtual image structure referencing the differencejournal; and synthesizing the virtual image of the data storage at thePiT using a first snapshot as a baseline.
 15. The Computer programproduct of claim 11, wherein the difference journal stores datadifferences between a first snapshot and a second snapshot, wherein ifdata changed a single time between the first snapshot and the secondsnapshot, the difference journal does not store the data changed.